Abstract
INTRODUCTION: Fibromyalgia is characterized by chronic widespread pain accompanied by reduced levels of physical activity and associated comorbidities such as overweight and obesity which have been associated to sarcopenia development. The aim of this systematic review is to ascertain whether Europeans with fibromyalgia show a reduction in sarcopenia determinants compared to apparently-healthy controls and to determine the risk of sarcopenia and its possible risk factors (PROSPERO: CRD42023439839). EVIDENCE ACQUISITION: Systematic searches were conducted on six databases (Academic-Search-Ultimate, CENTRAL, PubMed, SciELO, WOS-Core Collection, and ClinicalTrials.gov last-search February-2024) looking for original studies developed in European countries which assessed any of the sarcopenia determinants proposed by the EWGSOP2-guidelines (handgrip strength, five sit-to-stand, appendicular skeletal mass [ASM], skeletal muscle index [SMI]) and included fibromyalgia and healthy-control individuals. Studies mixing fibromyalgia with other diagnoses were excluded. Random-effects meta-analyses and meta-regressions were used to analyze possible differences and associated risk factors. The risk of bias was assessed using the Cochrane-Rob tool and the Quality Assessment Tool for Observational Studies, and the certainty of the evidence using GRADE-approach. EVIDENCE SYNTHESIS: A total of 25 studies (6393 individuals; 97% women; 20-65 years) were included. Fibromyalgia individuals showed reduced muscle strength ([handgrip] SMD: -1.16 [-1.29, -1.03]; high-certainty; [five sit-to-stand] not-assessed) and muscle quantity ([ASM] mean-difference: -0.83 kg [-1.41, -0.37]; [SMI] mean-difference: -0.26 kg/m(2) [-0.41, -0.10]; both low-certainty) compared to healthy-controls. Fibromyalgia individuals had nine-times greater risk for probable sarcopenia (OR: 9.23 [6.85, 12.45]; high-certainty), but not for confirmed sarcopenia ([ASM] OR: 0.91 [0.49, 1.67]; [SMI] OR: 0.67 [0.19, 2.33]; both low-certainty) according to the EWGSOP2 cut-off points. Reduced muscle strength was strongly associated to fibromyalgia-severity (β=-0.953 [-0.069, -0.038]). Studies were rated as high-risk of bias overall because did not account for some potential confounders (physical activity, sedentary time, Body Mass Index) which could influence the estimated effect. CONCLUSIONS: Europeans with fibromyalgia have a large reduction in muscle strength and may have a reduction in muscle quantity. The risk of probable sarcopenia according to the EWGSOP2 cut-off points was nine-times higher, but may have no difference in risk of reduced muscle quantity relative to healthy-controls. Muscle strength was strongly associated to disease severity.